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Abstract:

An optical device with a deformable membrane including an anchor zone on
a support contributing to trapping fluid, a central zone reversibly
deforming from a rest position, and an actuating mechanism to displace
fluid acting on the membrane in an intermediate zone between the anchor
and central zones. The actuating mechanism includes a principal actuation
mechanism and supplementary actuation mechanism each arranged in at least
one ring mounted around the central zone, each ring including one or
plural piezoelectric actuators, and being anchored on the intermediate
zone, only the supplementary actuation mechanism may be anchored to the
support, these actuation mechanisms and the membrane to which they are
anchored forming at least one piezoelectric bimorph, such that they
contract or expand in the radial direction during actuation such that
when the fluid moves, it deforms the central zone.

Claims:

1-23. (canceled)

24. An optical device with a deformable membrane comprising: an anchor
zone on a support contributing to trapping a quantity of liquid or
gaseous fluid; a central zone capable of reversibly deforming from a rest
position; actuation means to displace the fluid acting on the membrane in
an intermediate zone between the anchor zone and the central zone,
wherein the actuation means comprises principal piezoelectric actuation
means arranged in at least one ring mounted around the central zone, each
ring comprising one or plural piezoelectric actuators, and supplementary
piezoelectric actuation means arranged in at least one ring mounted
around the central zone and that surround the principal actuation means,
each ring comprising one or plural piezoelectric actuators, the principal
piezoelectric actuation means being anchored only to the intermediate
zone of the membrane, the supplementary piezoelectric actuation means
being anchored to the intermediate zone and possibly to the support, the
principal piezoelectric actuation means, the supplementary piezoelectric
actuation means, and the membrane to which they are anchored forming at
least a piezoelectric bimorph, the principal piezoelectric actuation
means and the supplementary piezoelectric actuation means contracting or
expanding in the radial direction during actuation so as to generate a
displacement of the fluid from the intermediate zone to the central zone
of the membrane or vice versa aiming at deforming the central zone
relative to its rest position.

25. An optical device according to claim 24, wherein the principal
actuation means and the supplementary piezoelectric means can be actuated
independently, simultaneously, or successively.

26. An optical device according to claim 24, wherein when there are
plural rings for the principal and/or supplementary piezoelectric means
they are mounted to be concentric to each other.

27. An optical device according to claim 24, wherein a piezoelectric of
the principal and/or the supplementary actuation means is in a form of a
continuous ring.

28. An optical device according to claim 24, wherein the piezoelectric
actuators of a single ring are in a form of ring sectors or rods oriented
in the radial direction with intervals between each other, the ring being
in pieces or continuous.

29. An optical device according to claim 28, wherein plural piezoelectric
actuators in a single ring or nearby rings share a same block of
piezoelectric material.

30. An optical device according to claim 25, wherein the supplementary
actuation means is directly or indirectly anchored to the support.

31. An optical device according to claim 24, wherein the actuation means
is anchored to a face of the membrane in contact with the fluid and/or on
a face of the contactless membrane of the fluid and/or are integrated in
the membrane.

32. An optical device according to claim 24, wherein the membrane
comprises a reinforcement layer at the intermediate zone, at least
locally, such that the intermediate zone at this reinforcement layer is
stiffer than the central zone.

33. An optical device according to claim 24, wherein the membrane
comprises a continuous layer at the central zone that occupies the
intermediate zone and the anchor zone.

34. An optical device according to claim 24, further comprising means for
compensating for a variation of focal distance of the optical device as a
function of temperature.

35. An optical device according to claim 34, wherein the compensation
means is coincident 30 with the piezoelectric actuator(s) of a ring.

36. An optical device according to claim 34, wherein the compensation
means comprises one or plural thermal bimorph elements arranged in a ring
either anchored to the membrane at the anchor zone projecting on the
intermediate zone, or fixed to the support on the side of the membrane
opposite the fluid.

37. An optical device according to claim 24, wherein when the actuation
means comprises plural piezoelectric actuators, they can be actuated
separately from each other or all together simultaneously, or
simultaneously actuated by groups.

38. An optical device according to claim 24, wherein the actuation means
comprises one or plural piezoelectric actuators arranged in a ring with
an internal periphery and an external periphery, the ring extending over
one of its peripheries by piezoelectric actuators in bars oriented in the
radial direction.

39. An optical device according to claim 24, comprising one or plural
piezoelectric actuators arranged in a ring, anchored to the membrane in
the intermediate zone and possibly in the anchor zone, capable of
operating passively by direct piezoelectric effect and dedicated to
monitoring a deformation of the membrane.

40. An optical device according to claim 24, further comprising a
protective cap fixed to the support.

41. An optical device according to claim 40, wherein the cap includes an
opening at the central zone or is leak tight and traps another fluid.

43. An optical device according to claim 24, wherein each of the fluids
is a liquid chosen from among propylene carbonate, water, an index
liquid, an optical oil, or an ionic liquid or a gas chosen from among
air, nitrogen, helium.

44. An optical device according to claim 24, wherein the piezoelectric
material is made based on PZT, aluminium nitride, polyvinylidene fluoride
or one of its copolymers, trifluoroethylene, trifluoroethylene, zinc
oxide, barium titanate, lead niobate, sillenites, or bismuth titanate.

45. An optical device according to claim 24, wherein it is a lens or a
mirror.

46. A camera, comprising at least one optical device according to claim
24.

Description:

TECHNICAL FIELD

[0001] This invention relates to an optical device with a deformable
membrane trapping fluid and provided with means of actuating the membrane
of piezoelectric type to adjust the radius of curvature of the membrane
in its central part. Such an optical device with a deformable membrane
may be a liquid lens with a variable focal length, a liquid lens with
correction of optical aberrations for adaptative optics or a mirror with
variable focal length.

[0002] For example, liquid lenses can be used in portable telephones with
a camera or movie camera function. Many developments are underway,
particularly the autofocus function and the zoom function. An attempt is
then made to introduce these functions, to obtain the shortest possible
response time but also to reduce energy consumption during actuation and
to increase the variations in the focal length with a given energy
consumption, without making the manufacturing of such cameras complex.
More globally, an attempt is made to integrate constituents of these
miniature cameras as much as possible in order to reduce costs,
dimensions and energy consumption. These miniature cameras operating in
visible wavelength are called CCM (Compact Camera Modules). The most
advanced liquid lens technology for this application at the moment is the
technology based on the electro-wetting principle.

[0003] Another application relates to cameras working in the infrared
(IR). Progress in terms of integration is not as advanced, and in most
cases the optics are dissociated from the cameras. Several developments
are underway particularly including the integration of optics (creation
of a camera module), integration of the autofocus function, etc. The
associated technical solutions are not known at the moment, and need to
be defined.

[0004] In one deformable membrane mirror application, the membrane is
reflecting. An attempt may be made to adjust the focal distance of the
mirror and therefore its radius of curvature. Such a mirror can be used
in ophthalmology or in adaptative optics. Finally, these optical devices
that may be of the lens or the mirror type may be used to stabilise
images.

STATE OF PRIOR ART

[0005] Patent application FR 2 919 073 discloses an optical device
comprising a flexible membrane with an anchor peripheral zone on a
support, the membrane and the support trapping a given volume of fluid
and piezoelectric actuation means to displace the liquid at the central
zone of the membrane in order to deform the central zone of the membrane.
The volume is approximately constant within a given temperature range.
Actuation means are formed from a plurality of radial micro-beams that
are fixed on the support at one end, and the other end of which acts on
the membrane in a zone located between the central zone and the anchor
zone. One disadvantage of this configuration is that it is not compact
because the actuation means bear on the support. Another disadvantage is
that the optical performances of the device are not optimal for a given
size and a given energy consumption during actuation. Similarly, the
energy consumption during actuation for a given dimension and given
optical performances is high.

[0006] Other patent applications disclose optical devices with
piezoelectric actuator means. For example there is U.S. Pat. No.
4,802,746 in which a cylindrical element made of a piezoelectric material
is closed at both ends by walls made of an elastic material, the assembly
defining a cavity containing a solid elastic material.

[0007] In American U.S. Pat. No. 4,407,567, a lens with a variable focal
distance comprises a cavity communicating with an expansion chamber, the
cavity being delimited by a mobile wall anchored to a support.

[0008] International patent application WO 2008/076399 discloses a lens
with a variable focal distance in which the piezoelectric actuation means
transmit an actuation force approximately normal to the optical axis of
the device, to the membrane through a thrust ring that bears on the
membrane. Such an optical device is relatively thick because the
piezoelectric actuation means, the thrust ring, the membrane and the
cavity containing the liquid have to be stacked. The actuation means are
not anchored to the membrane.

[0009] International patent application WO 2007/017089 discloses an
optical device with correction of optical aberrations. A flexible
membrane contributes to trapping the liquid. The membrane is provided
with piezoelectric actuation means in an intermediate zone located
between an anchor zone and a central zone, in the form of a ring broken
down into several sectors. Each sector-shaped part will contract or
expand tangentially, the forces being applied in a plane approximately
normal to the optical axis of the device. Such actuation can deform the
membrane locally and non-symmetrically about the optical axis. The
membrane can deform, making bumps and troughs around the periphery so as
to make it undulating, to correct optical aberrations in the device. Such
actuation means are incapable of varying the thickness of the liquid
under the central zone of the membrane and therefore varying the focal
distance of the optical device.

[0010] Patent application WO2008/100154 shows an optical device comprising
a cavity containing a gel or elastomer type material closed by
transparent covers. Piezoelectric type actuation means cooperate with one
of the covers made of glass. The stiffness of this cover tends to reduce
the efficiency of actuation and since the material contained in the
cavity is a gel or elastomer, it does not provide the required counter
action when actuated to deform the central zone of the covers. The centre
of the membrane deforms the gel or the elastomer under the actuation
effect and this membrane has to be stiff in order to obtain a given
deformation. Such an optical device is not very efficient because it is
limited in terms of the achievable optical diameter.

PRESENTATION OF THE INVENTION

[0011] The purpose of this invention is to provide an optical device with
a deformable membrane such as a lens or a mirror that does not have the
above mentioned disadvantages, namely size, high energy consumption, and
poor actuation efficiency.

[0012] Another purpose of the invention is to provide an optical device
with a deformable membrane for which the deformed shape of the membrane
may be adjusted accurately as required, in which the deformation may or
may not be symmetric about an optical axis of the optical device.

[0013] Yet another purpose of the invention is to make a lens type optical
device that can easily be controlled by very quickly changing from an
image stabilisation function to an autofocus function and that can
perform these two functions independently of each other.

[0014] Yet another purpose of the invention is to make a lens type optical
device that, when installed in a camera, can give a zoom function due to
an increased optical power.

[0015] Yet another purpose of the invention is to provide an optical
device with a deformable membrane with active compensation as a function
of the temperature so as to keep the same focal distance even if the
ambient temperature varies.

[0016] To achieve this, this invention proposes that actuation means
should be formed from one or several piezoelectric actuators arranged in
a ring, anchored to the membrane in an intermediate zone located between
a central zone and anchor zone to the support, these actuation means not
being anchored to the support either directly or through the anchor zone.

[0017] More precisely, this invention is an optical device with a
deformable membrane with an anchor zone on a support contributing to
trapping a quantity of a liquid or gaseous fluid, a central zone capable
of reversibly deforming from a rest position, actuation means for
displacing the fluid acting on the membrane in an intermediate zone
between the anchor zone and the central zone. The actuation means
comprise principal piezoelectric actuation means arranged in at least one
ring around the central zone, each ring comprising one or several
piezoelectric actuators, and supplementary piezoelectric actuation means
arranged in at least one ring around the central zone, each ring
comprising one or several piezoelectric actuators, these principal
piezoelectric actuation means being anchored only on the intermediate
zone of the membrane, these supplementary piezoelectric actuation means
being anchored to the intermediate zone and possibly on the support,
these principal piezoelectric actuations means, these supplementary
piezoelectric actuations means and the membrane to which they are
anchored forming at least one piezoelectric bimorph, the principal
piezoelectric actuation means and the supplementary piezoelectric
actuation means contracting or extending in the radial direction during
actuation so as to cause displacement of said fluid from the intermediate
zone towards the central zone of the membrane or vice versa in order to
deform the central zone relative to its rest position.

[0018] The principal piezoelectric actuation means and the supplementary
piezoelectric actuation means are preferably actuated independently to
perform different functions.

[0019] As a variant, they may be actuated simultaneously or one after the
other so as to contribute to making a strong change in the focal length
to satisfy the requirements of a zoom function.

[0020] When the optical device comprises several rings for the principal
and/or supplementary piezoelectric actuation means, they are installed to
be concentric with each other.

[0021] A piezoelectric actuator of the principal and/or supplementary
piezoelectric actuation means may be in the form of a continuous ring.

[0022] As a variant, the piezoelectric actuators of a single ring may be
in the form of ring sectors or radially oriented rods with intervals
between each other, the ring being in pieces or continuous.

[0023] Several piezoelectric actuators in a single ring or nearby rings
may share the same block of piezoelectric material to facilitate
technological integration and management of residual stresses.

[0024] Supplementary actuation means may be directly or indirectly
anchored to the support, which leaves a large amount of latitude during
the design of the optical device.

[0025] The actuation means may be anchored to one face of the membrane in
contact with said fluid and/or on one face of the membrane without
contact with said fluid and/or be integrated into the membrane.

[0026] The membrane may comprise a reinforcement layer at least locally at
the intermediate zone such that the intermediate zone at this
reinforcement layer is stiffer than the central zone.

[0027] The membrane may comprise a continuous layer at the central zone
that occupies the intermediate zone and the anchor zone, which
contributes to guaranteeing a good seal.

[0028] The optical device may also comprise means of compensating a
variation in the focal distance of the optical device as a function of
the temperature, so that it can operate without any particular adjustment
within a temperature range for example between -20° C. and
+60° C.

[0029] The compensation means may be coincident with the piezoelectric
actuator(s) of a ring.

[0030] As a variant, the compensation means may comprise one or several
thermal bimorph elements arranged in a ring either anchored to the
membrane at the anchor zone projecting onto the intermediate zone, or
fixed to the support on the side of the membrane opposite said fluid.

[0031] When the actuation means comprise several piezoelectric actuators,
they can be actuated separately from each other or all together or they
can be actuated simultaneously in groups. This gives greater flexibility
to obtain a required deformation of the membrane in the central zone.

[0032] According to one advantageous configuration, the actuation means
may comprise one or several piezoelectric actuators arranged in a ring
with an internal periphery and an external periphery, the ring being
prolonged on one of its peripheries through piezoelectric actuators in
radially oriented rods.

[0033] The optical device may comprise one or several piezoelectric
actuators arranged in a ring, anchored to the membrane in the
intermediate zone and possibly in the anchor zone, capable of operating
passively by direct piezoelectric effect and dedicated to monitoring a
deformation of the membrane.

[0034] The optical device may also comprise a protective cap fixed on the
support. The cap may be provided with an opening at the central zone or
it may be leak tight and it may trap another fluid.

[0036] Each of the fluids may be a liquid chosen from among propylene
carbonate, water, an index liquid, an optical oil or an ionic liquid, or
a gas chosen from among air, nitrogen or helium.

[0037] The actuation means may be made based on a PZT, aluminium nitride,
polyvinylidene fluoride or one of its copolymers, trifluoroethylene,
trifluoroethylene, zinc oxide, barium titanate, lead niobate, sillenites
such as bismuth titanate.

[0038] The optical device may be a lens or a mirror.

[0039] This invention also relates to a camera that may comprise at least
one optical device thus characterised.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] This invention will be better understood after reading the
description of example embodiments given purely for information and in no
way limitative with reference to the appended drawings in which:

[0041] FIGS. 1A, 1B show top and sectional views of the principal
actuation means of a first example of an optical device useful for
understanding the invention;

[0042] FIGS. 2A to 2E show top views of different examples of the
principal actuation means of an optical device according to the
invention, these actuation means being distributed on a single ring;

[0043] FIGS. 3A to 3D show a top view of different examples of the
principal actuation means of an optical device according to the
invention, these actuation means being distributed on two concentric
rings, these figures also show an optical device according to the
invention with the principal actuation means and supplementary actuation
means, the supplementary actuation means not being anchored to the
support;

[0044] FIGS. 4A, 4B show a sectional view of the deformed membrane with
two inflection points and four inflection points respectively;

[0045] FIGS. 5A to 5D show a top view of different examples of optical
devices according to the invention in which the actuation means comprise
principal and supplementary actuation means, the supplementary actuation
means being anchored to the support;

[0046] FIGS. 6A to 6D show piezoelectric actuators in optical devices
according to the invention sharing a same block of piezoelectric
material, regardless of whether these actuators are placed on the same
ring or on distinct rings, FIG. 6E shows that the optical device is
provided with one or several piezoelectric actuators that can operate
passively by a direct piezoelectric effect and dedicated to monitoring
deformation of the membrane;

[0047] FIGS. 7A to 7C show sectional views of different configurations of
the anchor to the support of the supplementary actuation means;

[0048] FIGS. 8A, 8B, 8C show different configurations for the membrane of
an optical device according to the invention, the actuation means being
omitted;

[0049] FIGS. 9A to 9H show different configurations for the actuation
means and for the multi-layer membrane in an optical device according to
the invention, the supplementary actuation means only being shown in
FIGS. 9F to 9H;

[0050] FIGS. 10A to 10F show a top view of different arrangements between
the principal actuation means and a reinforcement layer, the
supplementary actuation means being visible in FIGS. 10C, 10E;

[0051] FIGS. 11A, 11B show the position of the actuation means to obtain
given inflection points on the membrane;

[0052] FIGS. 12A to 12E show different configurations of the support on
which the membrane of an optical device according to the invention is
anchored, only the principal actuation means being visible;

[0053] FIGS. 13A, 13B show an optical device according to the invention
provided with means of compensating for a variation in its focal distance
due to a temperature variation, the supplementary actuation means not
being shown to avoid cluttering the figures;

[0054] FIGS. 14A to 14G show different steps in manufacturing an optical
device useful for understanding the invention;

[0055] FIGS. 15A, 15B show an optical device according to the invention
mounted in a camera.

[0056] Identical, similar or equivalent parts of the different figures
described below have the same numeric references to facilitate comparison
of different figures.

[0057] The different parts shown in the figures are not necessarily at the
same scale, to make the figures easier to read.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

[0058] FIGS. 1A and 1B show a first embodiment of an optical device useful
for understanding the invention. This optical device is made around an
axis called the optical axis XX'. It comprises a membrane 2, the
periphery of which is anchored in a leak tight manner on a support 1
which in this example is in the form of a dish. Therefore the membrane 2
comprises an anchor zone reference 2.3. The membrane 2 also comprises a
central zone 2.1 that corresponds to an optical field of the optical
device. It is materialised by dashed lines. The dish will collect a fluid
4 called the first fluid, this first fluid being a liquid or gas. More
generally, the membrane 2 and the support 1 contribute to forming a
cavity 3 in which the fluid 4 is trapped.

[0059] One of the faces of the membrane 2 is in contact with the fluid 4
contained in the cavity 3. The other face of the membrane 2 is in contact
with a second fluid 4' that may be ambient air. A variant will be
described later in which the second fluid 4' is trapped, it can be air or
another gas or even a liquid.

[0060] Membrane 2 means any flexible film acting as a barrier between the
first fluid 4 and the second fluid 4' on the side of the barrier opposite
to the first fluid 4.

[0061] If the optical device is a lens, the cavity 3 has a bottom 3.1 that
is transparent to an optical beam (not shown) that will propagate through
the lens. The membrane 2 is also transparent to the optical beam at least
in the central zone 2.1. If the optical device is a mirror, the membrane
2 is reflecting at least in its central zone 2.1.

[0062] The membrane 2 is capable of deforming reversibly from a rest
position under the action of a displacement of the fluid 4 contained in
the cavity 3 so as to vary the thickness of the fluid 4 at the central
zone 2.1 of the membrane 2 and thus curve this zone of the membrane. The
more flexible the membrane, the greater its deformation will be. The
fluid 4 contained in the cavity 3 is sufficiently incompressible so that
it can move towards the central zone 2.1 when a force is applied on the
membrane 2, this force being applied on the membrane 2 in an intermediate
zone 2.2 located between the central zone 2.1 and the anchor zone 2.3.
The fluid 4 has an approximately constant volume within a given
temperature range. The fluid 4 contained in the cavity acts as
"transmission" between the actuation means and the central zone of the
membrane. This fluid 4 may be a liquid or a gas.

[0063] In FIG. 1A it can be seen that the contour of the membrane 2 and
the support 1 are shown as being squares, while the central zone 2.1 is
shown as being circular. Obviously, these shapes are not limitative. The
membrane 2 and the support 1 could be circular, rectangular, ovoid or any
other shape and the central zone 2.1 could be square, rectangular, ovoid
or other.

[0064] Piezoelectric actuation means are provided to displace the fluid 4
from the cavity 3. They comprise so-called principal actuation means 5
that act on the membrane 2 in the intermediate zone 2.2. These actuation
means 5 are configured in at least one circular ring C mounted to be
concentric around the central zone 2.1, each ring C comprising one or
several piezoelectric actuators 5.1 visible in FIGS. 2A to 2D when there
are several of them. These piezoelectric actuation means are anchored
only on the intermediate zone 2.2 of the membrane 2. Each ring C extends
in a horizontal plane when the membrane is plane. If the membrane is
curved at the anchor, the piezoelectric actuators follow the curvature of
the membrane. The central zone 2.1 of the membrane may have a curvature
that is continuous with the curvature of the central zone during
actuation. But at rest, the curvatures of these two zones may be
different.

[0065] When the actuation means 5 are configured in several rings C as for
example can be seen in FIG. 3A, they are mounted to be concentric with
each other. In this FIG. 3A, it can be considered that one of the rings
can form the principal actuation means 5 and the other ring C may form
supplementary actuation means 5' that will be discussed later. This is
why the reference 5' is marked in dashed lines.

[0066] The principal actuation means and more particularly their
piezoelectric actuators 5.1 belonging to the same ring C deform radially
when they are actuated. They contract or extend in the radial direction
depending on the polarisation applied to them, this deformation having
the effect of changing the curvature of the membrane. In other words, the
difference between the outside radius and the inside radius of the ring C
varies at least locally when a piezoelectric actuator 5.1 is actuated.

[0067] It will be remembered that a piezoelectric actuator comprises a
block of piezoelectric material sandwiched entirely or partially between
two electrodes that when they are powered will apply an electric field to
the piezoelectric material. This electric field is used to control a
mechanical deformation of the block of piezoelectric material. The block
of piezoelectric material may be a single layer or multi-layer and it may
extend beyond an electrode. The electrodes on each side of a block of
piezoelectric material can be seen in FIGS. 6A, 6B. We have thus
described the inverse piezoelectric effect.

[0068] According to the invention, the principal actuation means 5 are
anchored only to the intermediate zone 2.2 of the membrane 2. Therefore
they do not have any anchor to the support 1. Nor are they anchored to
the central zone 2.1.

[0069] The supplementary actuation means 5' are anchored in the
intermediate zone 2.2 of the membrane but they may be anchored to the
support 1 or not anchored to the support 1.

[0070] These principal piezoelectric actuation means 5 and the membrane 2
on which they are anchored form at least one piezoelectric bimorph that
may either be heterogeneous or homogeneous. Remember that a piezoelectric
bimorph comprises a layer of piezoelectric material fitted with
electrodes attached to a layer that is a piezoelectric material when the
bimorph is homogeneous, or a non-piezoelectric material when the bimorph
is heterogeneous. In our case, this piezoelectric or non-piezoelectric
material layer is a layer of the membrane 2.

[0071] In FIGS. 1A, 1B, the principal actuation means 5 are shown
comprising a single piezoelectric actuator 5.1 in the form of a
continuous ring C. Of course, it is possible that the principal actuation
means 5 could comprise several elementary piezoelectric actuators 5.1
arranged in a ring, the ring C then possibly being discontinuous at the
piezoelectric material, or it could be continuous. Each of the elementary
piezoelectric actuators 5.1 may be in the form of a ring sector SC as
shown in FIGS. 2A, 2B, 2C. In FIG. 2A, there are four elementary
piezoelectric actuators 5.1, the ring being broken down into four sectors
SC, there are eight sectors SC in FIG. 2B, and in FIG. 2C there are
twenty-four. Instead of the elementary piezoelectric actuators 5.1 being
in the form of adjacent ring sectors, it is possible that they could be
in the form of rods B arranged in the radial direction in a ring as shown
in FIG. 2D. An attempt will be made to ensure that the space occupied by
the elementary piezoelectric actuators 5.1 located on the same ring C is
as large as possible in the intermediate zone so that the efficiency of
the actuation is as high as possible. In attempting to make the space
occupied by the rods B as large as possible and therefore that the space
between two adjacent rods B is as small as possible, there could be about
a hundred or even many more rods B in the ring C.

[0072]FIG. 2E shows the principal actuation means 5 arranged in two rings
fixed to each other. One of the rings, in the example the outer ring
Cext, comprises a single piezoelectric actuator which is continuous. The
other ring in the example, the inner ring Cint contains a plurality of
elementary piezoelectric actuators arranged in rods in the radial
direction. Each rod is connected to the outer ring Cext. It could be
envisaged that the continuous ring is broken down into pieces and
contains several elementary piezoelectric actuators. It would also be
possible for the outer ring to contain the plurality of rods instead of
the inner ring. Such configurations have the advantage that they increase
the efficiency of the optical device. This guarantees a significant
variation of the focal distance due to the continuous piezoelectric
surface while inclining the optical axis of the device, for example to
achieve an image stabilisation function due to the ring being broken down
into pieces.

[0073] It has already been mentioned that the principal actuation means 5
could be distributed in several rings C concentric around the central
zone 2.1. This variant is shown in FIG. 3A. In this configuration, there
is only one piezoelectric actuator 5.1 per ring C. In accordance with the
invention, the two rings C are fixed to the membrane 2 and are not
anchored to the support 1. They do not occupy any of the anchor zone 2.3
nor the central zone 2.1. It can be seen that this FIG. 3A can also
represent principal actuation means diagrammatically shown by one of the
rings C and supplementary actuation means diagrammatically shown by the
other ring C. In this configuration, the supplementary actuation means
are anchored to the membrane 2 only in the intermediate zone 2.2.

[0074] In a manner similar to what is described in FIGS. 2A to 2D, it is
possible that there are several elementary piezoelectric actuators 5.1 on
one ring C, and that there is a single actuator on another ring C or
other rings, as shown in FIGS. 3B and 3C. In FIG. 3B, the outer ring Cext
corresponds to a single piezoelectric actuator 5.1 that is continuous,
and the inner ring Cint contains several elementary piezoelectric
actuators 5.1, there are several blocks of piezoelectric material, the
ring being discontinuous. The reverse situation is shown in FIG. 3C, the
outer ring Cext contains several elementary piezoelectric actuators 5.1,
there are several blocks of piezoelectric material and the inner ring
Cint corresponds to a single piezoelectric actuator 5.1 and is
continuous. The discontinuous rings contain elementary piezoelectric
actuators 5.1 in the form of a ring sector. In FIG. 3D, the two rings
Cint, Cext contain several elementary piezoelectric actuators 5.1, they
are discontinuous, the elementary piezoelectric actuators 5.1 in one of
the rings referenced Cint, are in the form of a ring sector and the
elementary piezoelectric actuators 5.1 in the other ring Cext are in the
form of rods oriented in the radial direction. In all cases, the
piezoelectric actuator or the elementary piezoelectric actuators 5.1 of
one ring Cint, Cext, are anchored to the membrane 2 and do not have any
anchor with the support 1. This means that the rings extend over the
intermediate zone 2.2 but stop before the anchor zone 2.3 of the membrane
2, they do not occupy part of it nor the central zone 2.1.

[0075] With the principal actuation means 5 comprising several elementary
piezoelectric actuators 5.1, it is possible to obtain a deformed shape of
the membrane 2 in the central zone 2.1 that can be axisymmetric or
non-axisymmetric, however if the principal actuation means 5 comprise a
single piezoelectric actuator 5.1 per ring, the deformed shape of the
membrane 2 must be axisymmetric. Axisymmetric or non-axisymmetric means
symmetric or non-symmetric about the optical axis XX' of the optical
device.

[0076] When there are several elementary piezoelectric actuators 5.1 on a
single ring, they can be activated separately from each other or all
together simultaneously or they can be grouped into several groups of
adjacent or non-adjacent piezoelectric actuators and all piezoelectric
actuators in a group can be actuated simultaneously, each group being
actuated independently of another group.

[0077] The fact of obtaining a deformed shape of the membrane 2 in the
central non-axisymmetric zone 2.1 can give an advantageous dioptre to
achieve an image stabilisation function.

[0078] If the principal actuation means 5 comprise a mix of several
elementary piezoelectric actuators arranged in a discontinuous ring and a
piezoelectric actuator arranged in a continuous ring, the actuation
surface is increased while maintaining the possibility of a non
axisymmetric deformation. During actuation, the energy to deform the
membrane 2 is also higher than it is in the case in which there is only
one ring. Such a configuration is advantageous to combine focal distance
variation and image stabilisation functions. This is also true when the
principal actuation means correspond to one of the rings and the
supplementary actuation means correspond to the other ring.

[0079] FIGS. 4A, 4B show a sectional view of the deformed shape of the
membrane 2 after actuation of the principal actuation means in two
different modes. Note that FIGS. 4A and 4B do not show the actuation
means.

[0080] The deformed shape in FIG. 4A and FIG. 4B has two and four
inflection points 40 respectively, the inflection points 40 being shown
by stars. The deformed shape of the membrane 2 shown in FIG. 4A may be
obtained with the actuation means shown in FIG. 1A or in FIG. 3A.

[0081] Four inflection points 40 can be obtained using principal actuation
means 5 like described above and supplementary actuation means 5' as
shown in FIG. 5A.

[0082] The principal actuation means 5 are similar to those shown in FIG.
1A, in other words they are in the form of a piezoelectric actuator 5.1
arranged in a continuous ring. The supplementary actuation means 5' are
also formed from a piezoelectric actuator 5.1' arranged in a continuous
ring but now the ring is anchored firstly to the membrane 2 and secondly
to the support 1, it extends over the intermediate zone 2.2 and occupies
part of the anchor zone 2.3 of the membrane 2. The supplementary
actuation means 5' may have several elementary piezoelectric actuators
5.1' arranged in a discontinuous ring as shown in FIG. 5C. The elementary
piezoelectric actuator(s) 5.1' of the supplementary actuation means also
form a piezoelectric bimorph each with the membrane 2. The supplementary
piezoelectric actuation means 5', and the principal actuation means 5,
contract or expand in the radial direction when actuated so as to
generate a displacement of said fluid from the intermediate zone to the
central zone of the membrane or vice versa in order to deform the central
zone relative to its rest position.

[0083] The principal actuation means and the supplementary actuation means
may be controlled independently. The fact that the principal actuation
means and supplementary actuation means are provided gives a means of
making a fine adjustment to the deformation of the membrane in the
central zone. For example, actuation of the principal actuation means
makes it possible to perform an autofocus function that leads to an
axisymmetric deformation of the central zone of the membrane. Actuation
of the supplementary actuation means can perform an image stabilisation
function, which leads to a non-axisymmetric deformation of the membrane.
The two actuations may take place independently and successively.

[0084] Of course, the inverse could be envisaged, the principal actuation
means can perform the image stabilisation function, and the supplementary
actuation means can perform an autofocus function. Similarly, an optical
zoom application can be provided for example if actuation of the
principal actuation means perform an autofocus function which leads to a
limited amplitude deformed shape, the actuation of the supplementary
actuation means perform a zoom function when the two actuation means are
actuated simultaneously.

[0085] As a variant, the principal actuation means 5 may include several
elementary piezoelectric actuators 5.1 arranged in a discontinuous ring
while the supplementary actuation means 5' comprise a piezoelectric
actuator 5.1' arranged in a continuous ring as shown in FIG. 5B. Of
course, the principal actuation means 5 comprising several elementary
piezoelectric actuators 5.1 arranged in a discontinuous ring could also
be associated with supplementary actuation means 5' comprising several
elementary piezoelectric actuators 5.1' arranged in a discontinuous ring
as shown in FIG. 5D.

[0086] The principal or supplementary actuation means are positioned to be
offset from the required inflection points. When there are four
inflection points as shown in FIG. 4B, a ring is advantageously placed
between two adjacent inflection points.

[0087] FIGS. 6A, 6B show a section through the actuation means 5
comprising piezoelectric actuators 5.1 distributed on two rings Cint,
Cext, these piezoelectric actuators 5.1 share the same block of
piezoelectric material 50. Two sets of electrodes 51, 52 are drawn and
each set creates an electric field in the piezoelectric material 50 and
generates a mechanical deformation. The two sets of electrodes (51, 52)
are arranged in a ring and are placed concentrically. Such actuation
means 5 are equivalent to two series of piezoelectric actuators 5.1
positioned concentrically, each of the series comprising one or several
piezoelectric actuators as shown in FIG. 6B. Thus, the block of
piezoelectric material 50 only deforms locally at a set of polarised
electrodes. As shown in FIG. 6C, it could have been envisaged that the
actuation means 5 comprise several elementary piezoelectric actuators 5.1
arranged in a ring and that these piezoelectric actuators share the same
block of piezoelectric material 50 in the form of a continuous ring. Four
sets of discontiguous electrodes arranged in a ring sector are placed on
this block of piezoelectric material 50. FIG. 6C is a top view and shows
only a single electrode 51 in each set. FIG. 6D shows a top view of a
configuration of the actuation means 5 comprising a piezoelectric
actuator configured as an inner ring Cint and several elementary
piezoelectric actuators configured in a single outer ring Cext, the
actuators all sharing the same block of piezoelectric material 50. The
electrodes of the piezoelectric actuator of the outer ring are in a ring
while the electrodes of the elementary piezoelectric actuators of the
outer ring are in the form of a ring sector. Once again, in FIG. 6, one
of the rings Cint or Cext could act as the principal actuation means and
the other ring Cext or Cint could act as the supplementary actuation
means.

[0088] The coupling mode between the piezoelectric material and the
electrodes is shown transversely because it is easy to implement. The
piezoelectric material layer is sandwiched at least locally between one
or several pairs of electrodes. But of course, any other coupling mode,
for example longitudinal or shear, could be adopted.

[0089] Each pair of electrodes may be powered independently of the others,
which means that different voltages could be applied to all pairs of
electrodes. Thus, the deformation of the membrane 2 in the central zone
2.1 may be non-axisymmetric and there are many possible deformation
variations.

[0090] Therefore, the inverse piezoelectric effect will be used to control
deformation of the central zone 2.1 of the membrane 2.

[0091] The direct piezoelectric effect can be used to monitor deformation
of the membrane 2. The voltage that appears at the terminals of a
non-actuated elementary piezoelectric actuator can be acquired, while
other elementary piezoelectric actuators in the same ring are actuated.
It would also be possible to provide one or several piezoelectric
actuators capable of operating passively by a direct piezoelectric effect
arranged in a ring specially dedicated to this monitoring as shown in
FIG. 6E. The inner ring Cint is formed from at least one passive
piezoelectric actuator 70 detecting local deformation of the membrane by
direct effect. The actuation means 5 are formed from several elementary
piezoelectric actuators 5.1 arranged in an outer ring. These
piezoelectric actuators 5.1 can be actuated by the inverse effect. This
actuator is anchored to the membrane in the intermediate zone and
possibly in the anchor zone.

[0092] Of course, it would be possible that a single piezoelectric
actuator will deform the membrane intermittently and will monitor the
deformation of the membrane intermittently. It may thus be passive at
some times and active at others.

[0093] Yet another variant would be to use a strain gauge of another type
instead of a piezoelectric actuator to monitor deformation of the
membrane.

[0094] When the optical device is provided with supplementary actuation
means 5' anchored to the support 1, the anchor may be direct as shown in
FIGS. 7A and 7B or indirect as shown in FIG. 7c. In FIG. 7A, the
supplementary actuation means 5' are superjacent to the membrane 2, they
extend onto the intermediate zone 2.2 and the anchor zone 2.3 and extend
directly on the support 1. They do not have any contact with the fluid 4
trapped between the membrane 2 and the support 1. In FIG. 7B, they are
subjacent to the membrane 2 and in the same way extend over the
intermediate zone 2.2 and the anchor zone 2.3 and they prolong directly
onto the support 1.

[0095] In FIG. 7c, the supplementary actuation means 5' are superjacent to
the membrane 2, they extend over the intermediate zone 2.2 and the anchor
zone 2.3, possibly partially, but they do not occupy the support 1
directly. The principal actuation means are not shown in these FIGS. 7A,
7B, 7C for reasons of clarity.

[0096] We will now describe a few characteristics of the membrane 2 with
reference to FIGS. 8A to 8C. This membrane 2 comprises at least three
zones as we have already described called anchor zone 2.3, intermediate
zone 2.2 and central zone 2.1, in the direction from its edge towards its
centre. The intermediate zone 2.2 is the zone to which the actuation
means not shown are directly applied. The central zone 2.1 dedicated to
the optical field is deformed by movements of the fluid 4. Since this
deformation is reversible, the material in this central zone 2.1 will
operate in the elastic deformation range. Its transparency or on the
other hand its reflecting properties have already been mentioned above.
It is possible that the membrane 2 is single layer and homogeneous from
the central zone 2.1 as far as the anchor zone 2.3 (FIG. 8A). As a
variant, it may be multi-layer as shown in FIG. 8B, the two layers being
referenced 2a, 2b. It has two superposed layers 2a, 2b in the central
zone 2.1, in the intermediate zone 2.2 and in part of the anchor zone
2.3. In this anchor zone 2.3 the superjacent layer 2a of the stack is
prolonged directly on the support 1 beyond the subjacent layer 2b.

[0097] The anchor zone 2.3 of the membrane 2 must have bond properties on
the support 1. The superjacent layer 2a in FIG. 8B may be chosen to have
better bond properties on the support 1 than the subjacent layer 2b.

[0098] The intermediate zone 2.2 of the membrane 2 may have properties
that accentuate the deformation induced by the actuation means, which
means that it will preferably be chosen to be stiffer than the central
zone 2.1. In fact, there is interaction between the actuation means and
the membrane 2 itself. The membrane 2 contributes to actuation, and it
forms bimetallic strip with each piezoelectric actuator. It is thus
possible that the intermediate zone 2.2 is multi-layer and there are
several possibilities about the position of the actuation means relative
to the different layers of the intermediate zone 2.2.

[0099] The membrane 2 may be heterogeneous with at least one principal
layer 2b that occupies the central zone 2.1 and in some configurations
extends over the entire surface of the membrane 2 and at least one
reinforcement layer 2c that only extends over part of the membrane 2,
including at least the intermediate zone 2.2. In FIG. 8C that shows this
case, the principal layer 2b extends over the entire surface of the
membrane 2 and the reinforcement layer 2c in this example extends on the
anchor zone 2.3 and on the intermediate zone 2.2. The reinforcement layer
2c occupies part of the support 1 directly in the same way as in FIG. 9B
with layer 2b. In FIGS. 9A, 9B, 9C, the membrane 2 comprises a continuous
principal layer 2b that extends over its entire surface, but this is not
an obligation as will be seen later.

[0100] The principal or supplementary actuation means may be subjacent to
the membrane 2 and be in contact with the fluid 4 that it traps in
cooperation with the support 1, or it may be superjacent to the membrane
2, or it may be integrated into the membrane 2 that is then multi-layer.

[0101] When the principal or supplementary actuation means are distributed
on several rings, the piezoelectric actuators arranged on the different
rings are not necessarily all positioned in the same location relative to
the membrane 2. We will consider the various possible positions for the
actuation means 5, 5' relative to the membrane 2, with reference to FIGS.
9A to 9H. There are other possibilities. FIGS. 9A to 9E show actuation
means being the principal actuation means 5 comprising one or several
piezoelectric actuators arranged in a single ring, and consequently they
are not anchored to the support 1. They are only anchored to the
intermediate zone 2.2 of the membrane 2.

[0102] In FIG. 9A, the membrane 2 comprises a continuous layer 2b that
extends from the central zone 2.1 as far as the anchor zone 2.3, a
superjacent reinforcement layer 2c that only extends in the intermediate
zone 2.2. The actuation means 5 are arranged in a single ring, and are
superjacent to the reinforcement layer 2c. They are without contact with
the fluid 4 that the membrane 2 and the support 1 contribute to trapping.

[0103]FIG. 9B shows the continuous layer 2b that extends from the central
zone 2.1 to the anchor zone 2.3 and the actuation means 5 placed at the
intermediate zone 2.2 of the membrane 2 are sandwiched between the
continuous layer 2b and the reinforcement layer 2c. The reinforcement
layer 2c and the actuation means 5 are without contact with the fluid 4
that the membrane 2 and support 1 contribute to trapping. The
reinforcement layer 2c does not fully coincide with the actuation means 5
which extend beyond the reinforcement layer 2c. The opposite would be
possible, with the reinforcement layer 2c possibly extending beyond the
actuation means 5.

[0104]FIG. 9C shows the continuous layer 2b and the actuation means 5
placed at the intermediate zone 2.2 of the membrane 2 are sandwiched
between the continuous layer 2b and the reinforcement layer 2c. But in
this case the reinforcement layer 2c and the actuation means 5 are in
contact with the fluid 4 that the membrane 2 and the support 1 contribute
to trapping.

[0105] FIG. 9D shows the continuous layer 2b, and the reinforcement layer
2c placed at the intermediate zone 2.2 of the membrane 2 is sandwiched
between the continuous layer 2b and the actuation means 5. But in this
case the reinforcement layer 2c and the actuation means 5 are in contact
with the fluid 4 that the membrane 2 and the support 1 contribute to
trapping.

[0106] In FIGS. 9A, 9C and 9D, the reinforcement layer 2c and the
actuation means 5 have coincident surfaces. Of course, this is not an
obligation as can be seen in FIG. 9B. In FIG. 9E, there is a continuous
layer 2b and a reinforcement layer 2c sandwiched between the continuous
layer 2b and the actuation means 5. The reinforcement layer 2c extends
beyond the actuation means 5, it occupies part of the anchor zone 2.3. On
the other hand, it is preferable that it does not occupy part of the
central zone 2.1 to avoid making it too stiff.

[0107] FIGS. 9F, 9G, 9H show the principal actuation means 5 comprising
one or several piezoelectric actuators arranged in a ring without anchor
to the support 1, and supplementary actuation means 5' comprising one or
several piezoelectric actuators arranged in a ring anchored directly to
the support 1.

[0108] In FIG. 9F, the principal actuation means 5 and the supplementary
actuation means 5' are in contact with the fluid 4 trapped between the
membrane 2 and the support 1. They are both on the same side of the
reinforcement layer 2c that is superjacent to the continuous layer 2b.
The reinforcement layer 2c is between the actuation means 5, 5' and the
continuous layer 2b. The principal actuation means 5 and the
supplementary actuation means 5' are not contiguous and a space is formed
between them, the reinforcement layer 2c occupies this space and comes
into contact with the fluid 4 in this space. It can be seen that the
continuous layer 2b has no contact with the principal actuation means 5,
since there is a space formed between them. The reinforcement layer 2c
occupies this space. Thus, the continuous layer 2b has a variable
thickness, it is thicker at the central zone 2.1 than at the intermediate
zone 2.2 and the anchor zone 2.3.

[0109] In FIG. 9G, the supplementary actuation means 5' and the principal
actuation means 5 are not located on the same side of the reinforcement
layer 2c. The supplementary actuation means 5' are on the side of the
fluid 4 that the membrane 2 and the support 1 contribute to trapping. The
principal actuation means 5 are opposite the fluid 4 relative to the
reinforcement layer 2c. The continuous layer 2b extends from the central
zone 2.1 to the anchor zone 2.3 as in the example shown in FIG. 9F. Once
again, the reinforcement layer 2c occupies the space between the
principal actuation means 5 and the supplementary actuation means 5' and
the space between the principal actuation means 5 and the continuous
layer 2b.

[0110]FIG. 9H is yet another example of the membrane 2 in which the
principal actuation means 5 and the supplementary actuation means 5' are
not always on the same side of the reinforcement layer 2c. The principal
actuation means 5 are in contact with the fluid 4 trapped between the
support 1 and the membrane 2. The supplementary actuation means 5' are on
the side of the reinforcement layer 2c opposite the fluid 4. They are
anchored to the support 1 through the reinforcement layer 2c. Another
difference from the previous configurations is that the layer 2b at the
central zone 2.1 is not continuous as far as the anchor zone 2.3 as it
was before. It extends to the intermediate zone 2.2 but stops before the
anchor zone 2.3. Once again, this layer 2b that extends at the central
zone 2.1 is thicker at the central zone 2.1 than at the intermediate zone
2.2. The assembly between the reinforcement layer 2c and the layer that
occupies the central zone 2.1 must be sufficiently leak tight so that the
fluid 4 that the support 1 and the membrane 2 contribute to trapping
cannot escape from the cavity, even when the actuation means 5, 5' are
actuated.

[0111] In FIGS. 9F to 9H, the reinforcement layer 2c is common to the
principal actuation means 5 and the supplementary actuation means 5'. If
one of these actuation means comprises elementary piezoelectric actuators
arranged in a ring broken into several sectors or rods, it would be
possible that the reinforcement layer 2c could be continuous. It will be
seen later that as a variant, it may be discontinuous.

[0112] In all these examples, the layer 2b that occupies the central zone
and the reinforcement layer 2c are shown as being single layer, but it is
obvious that one or both of them could be multi-layer.

[0113] It is possible that the reinforcement layer 2c is not continuous as
shown in FIG. 10B or that it is partially discontinuous as shown in FIGS.
10D, 10F. In these configurations, the contour of the reinforcement layer
2c is approximately the same as the contour of the principal actuation
means 5.

[0114] FIG. 10A shows a top view of the principal actuation means 5 formed
from several elementary piezoelectric actuators 5.1 in ring sectors
arranged in a ring. FIG. 10B shows the reinforcement layer 2c that is
also broken down into four ring sectors, but it is larger because it
occupies part of the anchor zone 2.3. Its inside radius is approximately
the same as the inside radius of the ring of the principal actuation
means 5 while its outside radius is larger than the outside radius of the
principal actuation means 5. During assembly, the principal actuation
means 5 are superposed on the reinforcement layer 2c that is then
sandwiched between the layer 2b that extends in the central zone 2.1 and
the actuation means 5. The four sectors of the actuation means 5 are
superposed on the four sectors of the reinforcement layer 2c. The sectors
of the actuation means 5 do not project beyond the sectors of the
reinforcement layer 2c. The supplementary actuation means are not shown
in this configuration, in order to avoid cluttering the figures (FIGS.
10A, 10B).

[0115]FIG. 10c shows the principal actuation means 5 formed from
piezoelectric actuators 5.1 arranged in two rings, one on the inside
being continuous and the other on the outside being discontinuous and
broken into four sectors. The reinforcement layer 2c shown in FIG. 10D is
in the form of a ring for which the inside radius is approximately equal
to the inside radius of the inner ring and the outside radius of which is
larger than the outside radius of the outer ring of the actuation means.
In this configuration, it is assumed that the reinforcement layer 2c
occupies part of the anchor zone 2.3. The ring of the reinforcement layer
2c is provided with radial notches 20a open to the outside of the ring,
which are fixed in relation to the space separating two adjacent sectors
of the actuation means 5. These two FIGS. 10C and 10D may also represent
principal actuation means formed from one of the rings and supplementary
actuation means formed from the other ring.

[0116] FIG. 10E shows the principal actuation means 5 formed from several
piezoelectric actuators 5.1 arranged in two concentric rings, one on the
outside which is continuous and the other on the inside is discontinuous
and is broken down into eight sectors. The reinforcement layer 2c shown
in FIG. 10F is in the form of a ring for which the inside radius is
approximately equal to the inside radius of the inner ring and the
outside radius is approximately equal to the outside radius of the outer
ring of the actuation means 5. In this configuration, it is assumed that
the reinforcement layer 2c does not occupy part of the anchor zone 2.3.
The ring of the reinforcement layer 2c is provided with radial notches
20a open to the inside edge of the ring, which are fixed relative to the
space separating two adjacent sectors of the actuation means. These two
FIGS. 10E and 10F can also show the principal actuation means formed from
one of the rings and the supplementary actuation means formed from the
other ring.

[0117] The different configurations shown are not limitative and others
are obviously possible.

[0118] We will now explain how to obtain the deformation of the membrane
2, with reference to FIGS. 11A, 11B. The deformed shape of the membrane 2
shown in FIGS. 11A, 11B has two inflection points 40 in the radial
direction in the intermediate zone 2.2.

[0119] These two inflection points 40 can be obtained using the principal
actuation means 5 and the supplementary actuation means 5' as shown for
example in FIG. 5A.

[0120] In FIG. 11A, the principal actuation means 5 and the supplementary
actuation means 5' are on the same side of the membrane 2, in the example
on the same side as the fluid 4 trapped between the membrane 2 and the
support 1. During actuation, the electrodes associated with these
actuation means are polarised oppositely to obtain different curvatures
to the membrane 2. The piezoelectric actuator(s) of the principal
actuation means 5 is (are) elongated in the radial direction and the
piezoelectric actuator(s) of the supplementary actuation means 5' is
(are) contracted in the radial direction. The same effect can be obtained
by placing piezoelectric actuators of the principal actuation means 5 and
the supplementary actuation means 5' on each side of the membrane 2 and
by polarising the electrodes of the piezoelectric actuator(s) of one of
the actuation means in the same way as the electrodes of the
piezoelectric actuator(s) of the other actuation means. The piezoelectric
actuators of the principal actuation means 5 and the supplementary
actuation means 5' are deformed in the same way, either an elongation or
a contraction on the radial direction.

[0121] In FIGS. 11A and 11B, the membrane 2 is shown as being a single
layer, but of course it could be multi-layer, the actuation means
described in FIG. 11A could be transposed in the configuration in FIG.
9F. Similarly, the actuation means described in FIG. 11B could be
transposed in the configurations in FIG. 9G or 9H. The supplementary
actuation means are not shown in these FIG. 12 to avoid cluttering the
figures. Everything described in this figure obviously applies to an
optical device according to the invention.

[0122] The support 1 may be monolithic as shown at the beginning of this
description. As a variant shown in FIG. 12A, it could be formed by a
frame 1.5 fixed to a plate 1.1 to form the dish 3. The plaque 1.1
materialises the bottom of the dish 3 which is transparent to optical
radiation that will pass through it when the optical device operates in
transmission or is reflecting when the optical device operates in
reflection. There is no modification to the membrane 2 nor to the fluid 4
from what has been described above. The actuation means 5 are in the form
of a single piezoelectric actuator arranged in a ring.

[0123] The transparent plate 1.1 may have an approximately constant
thickness with approximately parallel plane faces as shown in FIG. 12A.
At least one face could be structured as shown in FIGS. 12B, 12C, 12D, in
which the outside face is convex or concave. The choice is made depending
on the required optical performances for the optical device. It allows
optical radiation to pass through the lens. The frame 1.5 may be made of
a semi-conducting material like silicon, which makes it possible to
integrate circuits associated with processing of the control of the
actuation means 5. The circuits are not shown, to avoid cluttering the
figures. The transparent plate 1.1 may be made of glass or plastic.

[0124] In FIGS. 12B, 12C, the transparent plate 1.1 has a convex structure
and in FIG. 12D it has a concave structure. The structure of the
transparent plate 1.1 may for example be obtained by machining or
moulding.

[0125] In FIG. 12E, the support 1 is materialised by the frame 1.5 and the
transparent plate 1.1 is replaced by a second membrane 200. The second
membrane 200 comprises a layer that has approximately the same surface as
the first membrane 2. The two membranes 2, 200 are anchored onto the
frame 1.5, each on one of its principal faces. They contribute to making
a housing for the liquid 4. This increases the optical performances of
the membrane 2. In the example described, the actuation means 5 are
provided on only one of the membranes 2. The other membrane 200 is not
actuated, but nevertheless it deforms when the actuation means 5 are
actuated. As a variant, the two membranes could be actuated.

[0126] It is possible that the membrane 2 provided with the actuation
means 5 is covered by a protective cap 201 sealed to the support 1 as
shown in FIG. 9H. This cap 201 delimits a cavity. For example, the
attachment can be made by molecular bonding, by organic bonding, by
anodic bonding, by eutectic bonding or an alloy layer for example made of
Au/Si or Au/Sn, for example being inserted between the cap 201 and the
support 1 to be sealed. These bonding techniques are currently used in
the microelectronics industry and in microsystems.

[0127] The cap 201 delimits a cavity 6 inside which a second fluid 4' is
trapped, the upper face of the membrane 2, in other words the face that
is not in contact with the first fluid 4, is in contact with the second
fluid 4'. At least the central part of the cap 201 and the second fluid
4' must be transparent to the incident optical radiation that will either
be reflected onto the membrane 2, or will pass through it depending on
the nature of the optical device.

[0128] The cap 201 may be made of glass or an organic material such as
polyethylene terephthalate PET, polyethylene naphthalate, polymethyl
methacrylate PMMA or polycarbonate PC if it is to transmit wavelengths in
the visible. The cap 201 protects the membrane 2 because such optical
devices with deformable membrane 2 are fragile objects that are difficult
to manipulate.

[0129] The optical device may be made by techniques known in
microelectronics. Thin layer deposition techniques such as chemical
vapour phase deposition, physical vapour phase electro-deposition,
epitaxy, thermal oxidation, evaporation and film lamination can be used.
Organic materials or gel sol type materials may be deposited by
sputtering with a spin coater. Moulding, embossing, heat embossing, nano
impression techniques may be used to structure the lower face of the
substrate as shown in FIGS. 12B to 12D. Bonding techniques may also be
used to bond the membrane 2 to the support 1 or to bond a bottom 3 to the
frame 1.5 or to bond cap 201 to the support 1, these techniques for
example can be chosen from among direct bonding, eutectic bonding, anodic
bonding, organic bonding. Thinning steps, for example by grinding,
chemical thinning or a combination of the two types could be performed
after bonding the bottom to the frame. The optical device can be
manufactured in batches and all caps 201 of the different devices may be
made collectively.

[0130] The membrane 2 may be made from organic materials such as
polydimethylsiloxane, polymethyl methacrylate, le polyethylene
terephthalate, polycarbonate, parylene, epoxy resins, photosensitive
polymers, silicones like those known under the name SiNR by Shin-Etsu or
WL5150 by Dow Corning or mineral materials such as silicon, silicon
oxide, silicon nitride, silicon carbide, polycrystalline silicon,
titanium nitride, diamond carbon, tin and indium oxide, aluminium,
copper, nickel.

[0131] Each of the fluids 4, 4' may be a liquid like propylene carbonate,
water, an index liquid, an optical oil or an ionic liquid or a gas for
example such as air, nitrogen, helium.

[0132] The piezoelectric material of the actuation means 5, 5' may be
chosen from among PZT or Lead Titano-Zirconate with formula
Pb(Zr.sub.x,Ti.sub.1-x)O3, aluminium nitride AlN, polyvinylidene
fluoride (PVDF) and its copolymers of trifluoroethylene (TrFE), zinc
oxide ZnO, barium titanate BaTiO3, lead niobate PNbO3, bismuth
titanate Bi4Ti3O12 or other sillenites that are oxides
with a metal/oxygen ratio equal to 2/3.

[0133] The deposition of a layer made of a piezoelectric material such as
PZT requires hot annealing at about 800° C. Often, the material
used in the membrane 2 will not resist these temperatures. Therefore, the
first step is to make piezoelectric material actuation means and to
assemble them to the membrane later. These constraints have to be taken
into account when creating the stack during manufacturing of the optical
device according to the invention.

[0134] The inventors realised that the focal distance of the optical
device might change in unwanted manner because the different materials
from which the optical device according to the invention is made do not
have the same coefficient of thermal expansion.

[0135] Therefore, means can be provided to compensate for a variation in
the focal distance due to a temperature variation. Refer to FIGS. 13A,
13B.

[0136] These compensation means 95 are formed from one or several thermal
bimorph elements 95.1 arranged in a ring, either at the membrane 2 at the
anchor zone 2.3 projecting onto the intermediate zone 2.2 as shown in
FIG. 13A, or at the bottom 3.1 of the dish 3 as shown in FIG. 13B. These
bimorph elements 95.1 are dedicated to this compensation. Under the
effect of an increase in the temperature that in particular causes an
increase in the volume of the fluid 4 trapped between the membrane 2 and
the support 1 and therefore unwanted deformation of the membrane 2, the
bimorph elements 95.1 deform to increase the volume of the dish 3 by
increasing its thickness. A bimorph element 95.1 formed from two
superposed layers made from materials with different coefficients of
thermal expansion will not cause any problem for those skilled in the
art.

[0137] In the configuration shown in FIG. 13B, the support 1 is similar to
the support shown in FIG. 12B. On the fluid side 4, the bimorph elements
95.1 are on the frame 1.5 and project onto the transparent plate 1.1. The
central part of the transparent plate 1.1 is concave and it comprises
striations at its periphery. An expansion joint 96 is inserted between
the plate 1.1 and the frame 1.5 to give its flexibility along the optical
axis and to enable an increase in the volume of the dish 3. The increase
in the volume of the dish 3 will be due to the deformation of the
membrane 2 around the edge of the anchor zone 2.3 and/or the support 1.
The objective is that expansion of the fluid 4 trapped between the
membrane 2 and the support 1 would not have any influence on the
deflection of the membrane 2 in the central zone 2.1 and therefore on the
focal distance of the optical device.

[0138] As a variant, the means 95 provided to compensate for a variation
in the focal distance under the effect of a temperature variation can be
made by the piezoelectric actuator(s) 5.1 arranged in at least one single
ring of the principal actuation means 5 or supplementary actuation means
5'. For example, it could be the piezoelectric actuator arranged
according to the ring Cint in FIG. 6B.

[0139] The next step is to make blocks of the piezoelectric actuators made
from piezoelectric materials as stacks of several piezoelectric materials
with appropriate coefficients of thermal expansion such that within the
range of working temperatures of the optical device, for example
-20° C. to +60° C., the blocks of piezoelectric material
offset the thermal expansion of the other materials in the optical
device, namely the support 1, possibly the cap if there is one and the
other block(s) of piezoelectric material, the first fluid 4 and the
second fluid 4' and of course the membrane 2. Of course, this
compensation will be made without applying an electric field to the
block(s) of piezoelectric material concerned.

[0140] It would also be possible that the means 95 for compensating a
variation of the focal distance under the effect of a temperature
variation could contribute to ensuring that the residual stress applied
to the membrane 2 remains approximately constant, regardless of the
climatic conditions. This thus avoids the development of buckling or
crimpling of the membrane 2 in the case of an excessive compressive
stress or an excessive tension stress that would have the effect of
degrading the performances of the optical device.

[0141] The material(s) in the membrane 2 is (are) chosen to satisfy the
requirements of the manufacturing method or so that the liquid lens or
the mirror achieves specific performances.

[0142] The efficiency of the optical device is better for a given energy
consumption if its central zone 2.1 is more flexible. A silicone organic
material is particularly suitable. It is then preferable that the
membrane should be made stiffer at the intermediate zone by providing the
reinforcement layer, for example made of a mineral material such as
silicon oxide and/or silicon nitride on the organic layer extending from
the central zone to at least the intermediate zone or even as far as the
anchor zone. A membrane for which the central zone 2.1 is made of silicon
oxide or silicon nitride would also be suitable.

[0143] It will also be arranged such that the actuation means once fixed
on the membrane 2 do not disturb the expected behaviour of the membrane
2. The deformed shape of the membrane 2 at rest must be compatible with
the required use of the optical device. At rest, the membrane 2 may form
an approximately plane, or concave or convex dioptre.

[0144] It will also be arranged such that the membrane at rest is subject
to a sufficiently low residual compression stress that does not cause any
crimpling or buckling. Similarly, at rest, the membrane tension stress
must be sufficiently low so that it can react efficiently to actuation of
the actuation means, which would not be the case if excessive tension
were applied to it. Therefore a compromise has to be found between
tension and compression stresses.

[0145] The reinforcement layer must be sufficient stiff to apply the
pressure applied by the actuation means onto the fluid trapped between
the membrane and the support, and therefore generate the required fluid
displacements. A list of materials that could be used for the
reinforcement layer is given below. They could be metallic materials such
as titanium, titanium nitride, aluminium of the order of few tens of
nanometers to a few micrometers thick for which the Young's modulus is
between a few tens of GPa and a few hundred GPa. It could be materials
such as silicon oxide, silicon nitride with a thickness of the order of a
few tens of nanometers to a few micrometers and for which the Young's
modulus is between a few tens of GPa to a few hundred GPa. Finally, it
may consist of organic materials such as photosensitive polymers and
particularly benzocyclobutenes (BCB) with a thickness of few micrometers
and for which the Young's modulus is a few GPa.

[0146] We will now consider an example of a manufacturing method of an
optical device with variable focal distance according to the invention.
We will use a sacrificial layer. Refer to FIGS. 14A to 14G.

[0147] The starting point is a substrate 100 in which a dish 3 was etched.
The substrate 100 may for example be made of glass (FIG. 14A). It forms
the support. A sacrificial material 101 is deposited in the dish 3 (FIG.
14B). The sacrificial material 101 may be organic, for example a
photosensitive resin, or a mineral material such as silicon oxide.

[0148] The membrane 2 is formed on the sacrificial material 101, such that
it projects over the edge of the dish 3 and is anchored to it (FIG. 14C).
A material chosen from the materials listed above could be deposited for
the membrane 2. The deposit can be made with a spin coater or by chemical
vapour phase deposition.

[0149] The next step is to form the actuation means 5 at the contactless
intermediate zone with the support 1 (FIG. 14D). They are deposited by
techniques used in micro-systems such as thin layer deposition,
lithography, etching. The next step is to release the membrane 2 by
eliminating the sacrificial material. This can be done by drilling at
least one hole 107 outside the optical field (central zone), in the
substrate 100 until the sacrificial material 101 is reached. The hole 107
passes through and opens up into the dish 3 (FIG. 14E). The elimination
may be chemical or thermal or it may be by oxygen plasma. The dish 3 is
then filled with the fluid 4 (FIG. 14F). Filling may be done by applying
a negative pressure to the dish 3 to facilitate penetration of fluid 4
and to prevent the formation of bubbles in the case of a liquid. Finally
the hole 107 is closed off so that the fluid 4 cannot escape (FIG. 14F).
An organic material could be used. The order of steps is not limitative.

[0150] The main actuation means 5 could also be formed for example after
the membrane 2 has been released, before or after filling. They could
also be formed on the sacrificial layer 101 before the membrane 2 is
formed, if they are eventually to be on the side of the fluid 4 trapped
between the support 1 and the membrane 2. In such a configuration, the
membrane 2 is superjacent to the actuation means 5. The supplementary
actuation means could, of course, be formed in the same way as the
principal actuation means. They are not shown in FIG. 12 to avoid
cluttering the figures.

[0151] If it required that the membrane 2 at rest should be curved,
concave or convex, an appropriate curvature is given to the free face of
the sacrificial layer 101, because it acts as a mould for the membrane 2.
Another solution for obtaining a curved membrane 2 would be to make it
buckle after releasing it. Buckling could be thermal. The controlling
parameters are then the difference between the coefficients of thermal
expansion of the membrane 2 and the substrate and the deposition
temperature of the membrane 2.

[0152] The membrane 2 could be protected by making the optical device
according to the invention by assembling a support 1 and a cap 201 as
described in FIG. 9H. There is no need for the cap 201 to be solid, and
in FIG. 14G it is recessed in its central part, and the opening is marked
as reference 202. A glue seal J is used to assemble the support 1 and the
cap 201.

[0153] Such an optical device with variable focal distance can be used in
a camera, and particularly a portable telephone camera. Refer to FIG.
15A. Such a camera comprises in cascade, an objective 80 including at
least one liquid lens type of optical device with variable focal distance
L according to the invention, an image sensor 81 for example of the CCD
or CMOS type supported on a substrate 82. In the example described, the
objective 80 comprises at least one lens 83 with fixed focal distance and
a liquid lens L according to the invention. In the following, this lens
with fixed focal distance 83 will be called the conventional optical
block. The liquid lens L is located between the conventional optical
block 83 and the image sensor 81. As a variant, the conventional optical
block 83 may be between the liquid lens L and the image sensor 81. The
conventional optical block 83 is static. As we have already seen, due to
its manufacturing method, the liquid lens L may be considered to be a
MOEMS (micro-optoelectromechanical system). The liquid lens L with
variable focal length is placed at a certain distance that depends on the
characteristics of the objective 80, the image sensor 81, but if this
distance is small, the liquid lens L and the image sensor 81 must be made
as a single component by integrating them using either the AIC (Above
Integrated Circuit) technology or the WLCSP (Wafer Level Chip Scale
Package) technology. The focal distance of the liquid lens L is adapted
by optimising the pressure of the liquid at rest but also the curvature
of the membrane 2 at rest and the liquid refraction index.

[0154] If the camera also includes a zoom function as shown in FIG. 15B,
an optical block 83 with at least two fixed focal length lenses 83.1,
83.2 and two liquid lenses L and L' will be used, one of which will be
between the two lenses 83.1, 83.2 of the optical block 83 and the other
close to the image sensor 81 as shown in FIG. 15B. In these FIGS. 15A,
15B, the optical devices according to the invention references L and L'
are represented very diagrammatically, their actuation means are not
shown.

[0155] With a given size of an optical device according to the invention,
the surface of the actuation means can be maximised by using several
piezoelectric actuators arranged in several rings. The energy provided by
the actuation means may be maximised, to either improve fluid
displacements and therefore the performances of the optical device with
constant power supply voltage, or to minimise the power supply voltage
for equivalent optical performances.

[0156] Configurations with several piezoelectric actuator rings at least
one of which comprises a single piezoelectric actuator and at least one
of which comprises several elementary piezoelectric actuators, can give a
high actuation power due to the single piezoelectric actuator in one of
the rings, and a non-axisymmetric deformation due to the elementary
piezoelectric actuators in another ring.

[0157] By anchoring the principal actuation means only to the membrane in
the intermediate zone, the size of the device can be made smaller than
would be possible with the configurations in which the actuation means
are anchored to the support.

[0158] Providing means of compensating for a variation of the focal
distance due to a temperature variation makes it possible to keep the
focal distance of the device constant regardless of the temperature,
within a given range.

[0159] Although several embodiments of this invention have been described
in detail, it will be understood that different changes and modifications
can be made without going outside the framework of the invention, and
particularly other methods could be used to make the membrane and the
actuation means.